Books
in black and white
Main menu
Share a book About us Home
Books
Biology Business Chemistry Computers Culture Economics Fiction Games Guide History Management Mathematical Medicine Mental Fitnes Physics Psychology Scince Sport Technics
Ads

Connection Oriented Networks - Perros H.G

Perros H.G Connection Oriented Networks - John Wiley & Sons, 2005. - 359 p.
ISBN 0-470-02163-2
Download (direct link): connectionorientednetworks2005.pdf
Previous << 1 .. 100 101 102 103 104 105 < 106 > 107 108 109 110 111 112 .. 181 >> Next

Length: This 8-bit field is populated with the length (in bytes) of the sub-object including the L, type, and length fields.
The format of the sub-objects for the IPv4 and IPv6 is shown in Figure 7.25. The field IPv4 address (respectively IPv6 address) in the IPv4 (IPv6) sub-object contains an IPv4 (IPv6) prefix whose length is given in the prefix length field. The abstract node represented by this sub-object is the set of all nodes whose IPv4 (IPv6) address has the prefix given in the IPv4 (IPv6) address field. Note that a prefix length of 128 indicates a single node.
The sub-object format for the autonomous system is the same as the one shown in Figure 7.24, with the sub-object contents consisting of a two-byte field populated with the autonomous system number. The abstract node represented by this sub-object is the set of all nodes belonging to the autonomous system.
0 1 0123456 7 8901 2345
L Type Length (Sub-object contents)
-// -
Figure 7.24 The format of a sub-object.
178
LABEL DISTRIBUTION PROTOCOLS
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 01
L Type Length IPv4 address
IPv4 address Prefix length Reserved
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 01
L Type Length IPv6 address
IPv6 address
IPv6 address
IPv6 address
IPv6 address Prefix length Reserved
Figure 7.25 The format of the sub-object for IPv4 and IPv6 prefixes.
The RECORD ROUTE object (RRO)
The existence of loose routes through an abstract node means that it is possible that loops can be formed particularly during periods when the underlying routing protocol is in a transient state. Loops can be detected through the RECORDROUTE object. In this object the IP address of each node along the path can be recorded. Also, the labels used along the path can be recorded. The RECORD ROUTE object can be present in both Path and Rev messages.
The RECORD ROUTE object class is 21 and there is one object type, -Type 1. The object contents consists of a series of variable-length sub-objects organized in a last-in-first-out stack. Three different sub-objects have been defined: the IPv4 sub-object, the IPv6 sub-object, and the label sub-object. The first two sub-objects are the same as the IPv4 and the IPv6 sub-objects defined above in the EXPLICIT ROUTE object and shown in Figure 7.22 (with the exception that the reserved field has been replaced by a flags field.) The label sub-object has the structure shown in Figure 7.24, and it contains the entire contents of the LABEL object.
The SESSION_ATTRIBUTE object
This object contains setup holding priorities for an LSP, plus various flags. The setup priority is the priority used for allocating resources. The holding priority is the priority used for holding onto resources.
7.4.3 The RSVP-TE Path and Resv Messages
The RSVP-TE Path and Resv message are similar to those in RSVP. The RSVP-TE Path message consists of the common header shown in Figure 7.20 followed by the objects:
INTEGRITY (optional)
SESSION
PROBLEMS
179
RSVPHOP
TIME_VALUES
EXPLICIT ROUTE (optional)
LABELREQUEST
SESSION_ATTRIBUTE (optional)
POLICYDATA objects (optional)
A sender descriptor consisting of the SENDER TEMPLATE and the SENDER TSPEC
ADSPEC (optional)
RECORDROUTE (optional)
The RSVP-TE Resv message consists of the common header shown in Figure 7.20 followed by the objects:
INTEGRITY (optional)
SESSION
RSVPHOP
TIME_VALUES
RESV CONFIRM (optional)
SCOPE (optional)
POLICY DATA objects (optional)
STYLE
A style-dependent flow descriptor list. For the fixed-filter (FF) style, it consists of the objects: FLOWSPEC, FILTERSPEC, LABEL, RECORD ROUTE (optional). For the shared explicit (SE) style, it consists of the objects: FILTER SPEC, LABEL, RECORD ROUTE (optional).
7.4.4 RSVP-TE Extensions
RSVP was designed to support resource reservations for data flows defined between a sender and a receiver. As the number of data flows increases, the RSVP overhead on the network increases as well due to the continuous refreshing messages that have to be exchanged. Also, the memory required to store the path state information in each router and the amount of processing increases as well. In view of this, RSVP is not considered a protocol that scales up well. Similar problems arise in RSVP-TE, since it is based on RSVP.
Several solutions have been proposed to alleviate these problems. For instance, a mechanism for reliable delivery has been proposed that reduces the need for refresh messages. This mechanism makes use of two new objects, MESSAGE ID and MESSAGE ID ACK. Also, the amount of data transmitted due to refresh messages can be reduced by using the Srefresh message, a new summary refresh message.
Previous << 1 .. 100 101 102 103 104 105 < 106 > 107 108 109 110 111 112 .. 181 >> Next