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258 lines
14 KiB
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<meta name="DC.Title" content="Routing characteristics for frame relay" />
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<meta name="abstract" content="This topic provides information about how data is routed through a frame-relay network." />
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<meta name="description" content="This topic provides information about how data is routed through a frame-relay network." />
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<title>Routing characteristics for frame relay</title>
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<body id="rzak3formats"><a name="rzak3formats"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Routing characteristics for frame relay</h1>
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<div><p>This topic provides information about how data is routed through
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a frame-relay network.</p>
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<div class="section"><p>The frame-relay network routes frames through
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the network by examining the data link connection identifier (DLCI) field
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and then routing the frame to an outgoing link. The network delivers frames
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to the remote terminal equipment (TE) in the same sequence as they were provided
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to the network by the local TE.</p>
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</div>
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<div class="section"><p>At each node within the frame-relay network, the system verifies
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the frame check sequence (FCS) and checks the frame format and size. If the
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frame is valid, the system replaces the DLCI and FCS before routing the frame
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to the next node. If the frame is damaged or otherwise not valid, the system
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discards it. The network node provides no error recovery.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Frame-relay core services frame format</h4></div>
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<div class="section"><p>The following figure shows the basic frame format that is used
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for frame-relay communications.</p>
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</div>
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<div class="example"><div class="fignone"><span class="figcap">Figure 1. Frame format that frame-relay networks use</span><br /><img src="rzak3510.gif" alt="Frame format that frame-relay
networks use" /><br /></div>
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</div>
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<div class="section"><p>The frame-relay core services (FRCS) portion of the frame routes
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the frame through the frame-relay network. The frame structure is based on
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the ITU-T Q.922 protocol.</p>
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</div>
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<div class="section"><p><a href="#rzak3formats__rzak3frcsfig">Figure 2</a> shows the FRCS
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frame format on the fields within the 2-byte Q.922 address field (QA).</p>
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</div>
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<div class="example"> <div class="fignone" id="rzak3formats__rzak3frcsfig"><a name="rzak3formats__rzak3frcsfig"><!-- --></a><span class="figcap">Figure 2. Frame format for frame-relay core
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services (FRCS)</span><br /><img src="rzak3504.gif" alt="The QA portion of the frame
includes: DLCI0 = DLCI high order bits (6 bits); DLCII = DLCI low order bits
(4 bits); C/R = Command/response bit (not used); EA0/1 = Extended address
indicators; CC = Congestion control (3 bits)." /><br /></div>
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</div>
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<div class="section"><h4 class="sectiontitle">Frame-relay protocol headers</h4></div>
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<div class="section"><p>TEs use frame-relay protocol headers to provide routing for frames,
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to assure data integrity, and to perform recovery when frames are damaged
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or lost. iSeries™ frame-relay
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support uses protocol headers that are defined in Frame-Relay Forum IA 3.1.</p>
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</div>
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<div class="section"><p>The IBM<sup>®</sup> <span><img src="eserver.gif" alt="eServer" /></span> iSeries system
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uses protocol header formats for Systems Network Architecture (SNA) direct,
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bridged local area network (LAN), and local management interface (LMI) connections.
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The information field of the FRCS frame contains these headers and information
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fields (protocol data units or IP packets).</p>
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</div>
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<div class="section"><p>The following figures show the protocol header
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formats.</p>
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</div>
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<div class="example"><div class="fignone"><span class="figcap">Figure 3. SNA direct frame format</span><br /><img src="rzak3518.gif" alt="SNA direct frame format" /><br /></div>
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</div>
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<div class="example"> <div class="fignone"><span class="figcap">Figure 4. IP direct frame format</span><br /><img src="rzak3517.gif" alt="IP direct frame format" /><br /></div>
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</div>
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<div class="example"><div class="fignone"><span class="figcap">Figure 5. High-Performance Routing (HPR) frame format</span><br /><img src="rzak3516.gif" alt="High-Performance Routing
(HPR) frame format" /><br /></div>
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</div>
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<div class="example"><div class="fignone"><span class="figcap">Figure 6. Bridged token-ring and DDI LAN frame format (Frame-Relay
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Forum IA 3.1)</span><br /><img src="rzak3513.gif" alt="Bridged token-ring and DDI
LAN frame format (Frame-Relay Forum IA 3.1)" /><br /></div>
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</div>
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<div class="example"><div class="fignone"><span class="figcap">Figure 7. Bridged IEEE Ethernet LAN frame format (Frame-Relay Forum
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IA 3.1)</span><br /><img src="rzak3512.gif" alt="Bridged IEEE Ethernet LAN
frame format (Frame-Relay Forum IA 3.1)" /><br /></div>
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</div>
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<div class="example"><div class="fignone"><span class="figcap">Figure 8. Bridged Ethernet version 2 LAN frame format (Frame-Relay
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Forum IA 3.1)</span><br /><img src="rzak3514.gif" alt="Bridged Ethernet version
2 LAN frame format (Frame-Relay Forum IA 3.1)" /><br /></div>
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</div>
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<div class="example"><div class="fignone"><span class="figcap">Figure 9. LMI message frame format</span><br /><img src="rzak3515.gif" alt="LMI message frame format" /><br /></div>
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</div>
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<div class="example"><div class="fignone"><span class="figcap">Figure 10. Address Resolution Protocol (ARP) format</span><br /><img src="rzak3519.gif" alt="Address Resolution Protocol
(ARP) format" /><br /></div>
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</div>
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<div class="section"><p><a href="#rzak3formats__rzak3formatfield">Table 1</a> describes
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the protocol header fields.</p>
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</div>
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<div class="tablenoborder"><a name="rzak3formats__rzak3formatfield"><!-- --></a><table cellpadding="4" cellspacing="0" summary="" id="rzak3formats__rzak3formatfield" class="singleborder" frame="border" border="1" rules="all"><caption>Table 1. Format fields for the frame-relay protocol header</caption><thead align="left"><tr><th align="left" valign="top" width="33.33333333333333%" id="d0e155">Field</th>
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<th align="left" valign="top" width="33.33333333333333%" id="d0e157">Description</th>
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<th align="left" valign="top" width="33.33333333333333%" id="d0e159">Values and notes</th>
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</tr>
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</thead>
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<tbody><tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 ">C</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Q.922 (HDLC) control field</td>
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<td valign="top" width="33.33333333333333%" headers="d0e159 "> </td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 ">PAD</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Pad characters</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e159 ">Pad characters (hex 00) are permitted between
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the control field and the NLPID field. Pad characters are used for boundary
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alignment.</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 ">NLPID</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Network-level protocol identifier</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e159 "> <dl><dt class="dlterm">08</dt>
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<dd>ITU-T Q.931 (SNA direct and HPR)</dd>
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<dt class="dlterm">80</dt>
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<dd>IEEE Subnetwork Access Protocol (SNAP) for bridged LAN connections</dd>
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<dt class="dlterm">CC</dt>
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<dd>Internet Protocol (IP) direct</dd>
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</dl>
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</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 ">PD</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Protocol discriminator</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e159 ">LMI frames use hex 08</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 ">OUI</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Organization-unique identifier</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e159 "> <dl><dt class="dlterm">0080C2</dt>
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<dd>IEEE 802.1</dd>
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<dt class="dlterm">000000</dt>
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<dd>ARP</dd>
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</dl>
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</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 ">PID</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Protocol identifier</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e159 ">The iSeries system supports the following
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formats not using frame check sequence (FCS): <dl><dt class="dlterm">0007</dt>
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<dd>Ethernet</dd>
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<dt class="dlterm">0009</dt>
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<dd>Token-ring network</dd>
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<dt class="dlterm">000A</dt>
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<dd>DDI network</dd>
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<dt class="dlterm">0806</dt>
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<dd>ARP</dd>
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</dl>
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The iSeries system provides receive-only support for
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the following formats using FCS: <dl><dt class="dlterm">0001</dt>
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<dd>Ethernet</dd>
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<dt class="dlterm">0003</dt>
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<dd>Token-ring network</dd>
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<dt class="dlterm">0004</dt>
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<dd>DDI network</dd>
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</dl>
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</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 ">L2</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Layer 2 protocol</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e159 ">For iSeries systems using SNA direct connections,
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4C80 is placed in the L2 field <p>Byte 1</p>
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<dl><dt class="dlterm">4C</dt>
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<dd>IEEE 802.2 (ISO 8802/2)</dd>
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<dt class="dlterm">4E</dt>
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<dd>Q.922 (IDLC)</dd>
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<dt class="dlterm">46</dt>
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<dd>LAP-B (X.25)</dd>
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<dt class="dlterm">4A</dt>
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<dd>HDLC NRM (SDLC)</dd>
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<dt class="dlterm">51</dt>
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<dd>ISO 7776</dd>
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<dt class="dlterm">70</dt>
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<dd>Without IEEE 802.2 (ISO 8802/2) header</dd>
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</dl>
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<p>Byte 2</p>
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<dl><dt class="dlterm">80</dt>
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<dd>Undefined</dd>
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<dt class="dlterm">81</dt>
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<dd>MAC address included (IEEE 802.2, ISO 8802/2) or HDLC address included
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(ISO 7776)</dd>
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</dl>
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</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 ">L3</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Layer 3 protocol</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e159 ">For iSeries systems using SNA direct connections,
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7082 is placed in the L3 field.<p>Byte 1</p>
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<dl><dt class="dlterm">66</dt>
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<dd>ITU-T X.25</dd>
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<dt class="dlterm">67</dt>
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<dd>ISO 8208 (X.25 PLC)</dd>
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<dt class="dlterm">70</dt>
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<dd>User-specified</dd>
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</dl>
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<p>Byte 2</p>
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<dl><dt class="dlterm">81</dt>
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<dd>SNA subarea (FID4)</dd>
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<dt class="dlterm">82</dt>
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<dd>SNA peripheral (FID2)</dd>
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<dt class="dlterm">83</dt>
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<dd>APPN (FID2)</dd>
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<dt class="dlterm">85</dt>
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<dd>HPR Network Layer Protocol (FID5)</dd>
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</dl>
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</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 "> </td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Information field</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e159 ">iSeries support for SNA direct, frame-relay
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connections requires the information field to contain a FID2 protocol data
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unit (PDU). <p>Information fields sent over bridged connections may contain
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FID2 PDUs or IP packets.</p>
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section"><div class="note"><span class="notetitle">Notes:</span> </div>
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<dl><dt class="dlterm">AC</dt>
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<dd>Access control</dd>
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<dt class="dlterm">FC</dt>
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<dd>Frame control</dd>
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<dt class="dlterm">DA</dt>
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<dd>Destination address</dd>
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<dt class="dlterm">SA</dt>
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<dd>Source address</dd>
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<dt class="dlterm">RI</dt>
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<dd>Routing information</dd>
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<dt class="dlterm">Lth</dt>
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<dd>Length</dd>
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<dt class="dlterm">Type</dt>
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<dd>Ethernet type</dd>
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<dt class="dlterm">DSAP</dt>
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<dd>Destination service access point</dd>
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<dt class="dlterm">SSAP</dt>
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<dd>Source service access point</dd>
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<dt class="dlterm">Ctl</dt>
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<dd>IEEE 802.2 control field</dd>
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</dl>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzak3overview.htm">Frame relay</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rzak3rzak3snadirconfig.htm" title="The IBM eServer iSeries system allows frame-relay connections to remote systems that support the Systems Network Architecture (SNA) direct format that is defined by the Frame-Relay Forum IA 3.1. In this format, the frame-relay packets encapsulate the SNA data.">SNA direct configurations</a></div>
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<div><a href="rzak3rzak3ipdirconfig.htm" title="The iSeries system allows frame-relay connections to remote systems that support the IP direct format defined by the Frame-Relay Forum IA 3.1. In this format, the frame-relay packets encapsulate the TCP/IP data.">IP direct configurations</a></div>
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<div><a href="rzak3rzak3bridged.htm" title="The iSeries system allows frame-relay connections to remote local area networks (LANs) that support the bridged frame-relay formats defined by the Frame-Relay Forum IA 3.1. Most bridges, routers, and communication controllers support these formats.">Bridged connections for frame relay</a></div>
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