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Enhanced Charging Service Overview

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Cisco ASR 5000 Series Product Overview ▄

OL-22938-02

Step 3

When a packet hits a ruledef that has x-header format configured in its charging-action, x-header insertion into that
packet is done using the given x-header-format.

Step 4

If x-header-insertion is to be done for fields which are marked as encrypt, the previously encrypted value is populated
for that field accordingly.

Limitations to the Header Insertion Feature

The following are limitations to insertion of x-header fields in HTTP headers:

The packet size is assumed to be less than ―Internal MED MTU size, the size of header fields inserted‖. Header

insertion does not occur after the addition of the fields, if the total length of packet exceeds the internal MTU
size.

Header insertion occurs for both HTTP GET and POST requests. However, for POST requests, the resulting

packet size will likely be larger than for GET requests due to the message body contained in the request. If the
previous limitation applies, then POST request will suffer a bigger limit due to this.

Header insertion does not occur for retransmitted packets.

Header insertion does not occur for packets with incomplete HTTP headers.

Header insertion does not occur for TCP OOO and IP fragmented packets.

Window size scaling is not handled in the case of header insertion. Header insertion does not occur if the

resulting packet after header insertion exceeds the advertised TCP window size of the server.

Currently only those x-header fields in header portion of application protocol that begin with ―-x‖ are parsed at

HTTP analyzer. In URL and data portion of HTTP any field can be parsed.

The following are limitations to insertion of x-header fields in WSP headers:

x-header fields are not inserted in IP fragmented packets.

In case of concatenated request, x-header fields are only inserted in first GET or POST request (if rule matches

for the same). X-header fields are not inserted in the second or later GET/POST requests in the concatenated
requests. For example, if there is ACK+GET in packet, x-header is inserted in the GET packet. However, if
GET1+GET2 is present in the packet and rule matches for GET2 and not GET1 x-header is still inserted in
GET2. In case of GET+POST also, x-header is not inserted in POST.

In case of CO, x-header fields are not inserted if the WTP packets are received out of order (even after proper re-

ordering).

If route to MMS is present, x-headers are not inserted.

x-headers are not inserted in WSP POST packet when header is segmented. This is because POST contains

header length field which needs to be modified after addition of x-headers. In segmented WSP headers, header
length field may be present in one packet and header may complete in another packet.

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